Magnetostrictive materials in Anti Shoplifting
Magnetostrictive materials are widely used in the Anti Shoplifting systems. Magnetostriction is the property of ferromagnetic materials that cause them to change the physical shape or dimensions during the process of magnetization. This variation in shape due to the application of magnetic field helps to change the magnetostrictive strain until reaching its saturation value.
In anti shoplifting, most of the tags used are AM means Acousto-Magnetic and are very much able to protect the wide exits & allow the high speed label applications. It uses the transmitter to transmit the frequency approximately at 58 KHz in pulses in a zone under surveillance. As soon as the pulse ends, the AM tags responds by emitting a single frequency same as a tuning fork (The frequency of a tuning fork depends on its dimensions and the material from which it is made) & the transmitter is off between the pulses, and the signal transmitted is detected by the label. The microchip checks the signal to ensure that the frequency is right & synchronized with the receiver at the correct level & repetition rate. If the criteria meet, an alarm is activated.
Magnetostrictive materials convert magnetic energy into kinetic energy, or the reverse. The property can be quantified by the magnetostrictive coefficient, which may be positive or negative and is defined as the fractional change in length as the magnetization of the material increases from zero to the saturation value. The effect is responsible for the electric hum which can be heard near transformers and high power electrical devices.
AM materials are highly magnetostrictive as the tag material shrinks in the magnetic field. The higher magnetic field lets to make the metal smaller, hence directly proportional. Usually the metal shrinks by 1/1000th of an inch over its full 1.50 inch length.
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